Micromechanical pressure sensors are frequently composed of different components (such as substrate, base, housing), which are joined together and have different thermal expansion coefficients, as illustratively described in German Patent Application No. DE 103 30 252 A1. In this context, different thermal expansions may lead to thermal stresses, which negatively affect the junctions or also the functional elements of a pressure sensor, such as the diaphragm and/or the strain gauge. This may result in corruption of the measured signal or increased susceptibility of the pressure sensor to mechanical destruction.
German Patent No. DE 41 30 044 C2 describes a semiconductor pressure sensor having a silicon substrate, a diaphragm formed from the substrate, strain gauges, as well as a base joined to the substrate. There, the substrate and the base have different thermal expansion coefficients. In order to prevent an unwanted signal component in the strain gauges caused by different thermal stresses in the substrate and the base, an octagonal diaphragm is produced in the substrate, the octagonal diaphragm uniformly distributing the thermal stress in the diaphragm.
A further way to compensate for corruption of the measured signal caused by thermally induced thermal stresses is described in the publication H. A. Kayal et al., “Anwendungsspezifische intelligente Sensoren” (Application-Specific Intelligent Sensors), Elektronik (Electronics) 09/1988, pp.112–117. There, the temperature dependence of the measured signal is compensated using a complex integrated circuit.
World Patent WO 00/29824 and U.S. Pat. No. 6,229,190 B1 describe semiconductor elements having recesses next to the diaphragm and the diaphragm surround. These recesses are used to maximize the measured signal, which is acquired by piezoresistive elements, by preventing edge effects that can be observed upon mounting the diaphragm.
German Patent Application No. DE 101 56 406 A1 describes a method in which a pressure sensor is implemented using a strain gauge on a deformation sensor. The bond between the strain gauge and the surface of the deformation sensor is illustratively accomplished using low-melting glass (seal glass) or epoxy adhesive. Moreover, one exemplary embodiment shows that the deformation sensor has a steel body with a diaphragm at the extremity, and that the strain gauge is produced from a silicon wafer.